Metaphor
As revealed in the narrative, the misfit was not actually buried alive. This phrase occupies a section of the story where he recounts his ordeal and attempts to illustrate the extreme discomfort he faced in the penitentiary. He employs a metaphor, likening his experience there to being buried alive. A key insight to maintain during your readings and analysis of literary works is that whenever there are comparisons that are not literally true, it is likely you are encountering figurative language—specifically a metaphor.